When I turn on my PS3 my Samsung TV automagically turns on and switches to the appropriate input.

My Toshiba TV and my Onkyo receiver both support it. It's not a cost/licensing issue since it's built into HDMI and Pulse-Eight makes a USB CEC HDMI passthrough adapter and provides a libCEC library: http://www.pulse-eight.com/store/products/104-usb-hdmi-cec-a...

PS3 supports it. Although not when the youtube app is running for some reason. When I turn my TV on, the PS3 starts automatically and I can use the remote to navigate menus and Netflix.

Not all TVs support CEC or have it turned on by default.

My bluray player (a Sony from a couple years ago) does this perfectly fine with my Samgsung TV. So, some devices use it.

Works great between my Samsung HDTV and Panasonic BluRay player, both 3 years old. Only have to use one remote. :-)

Wii U gamepad has a TV button that turns the touchscreen into a remote control for my TV.

Not sure, but XBMC supports it.